Line sawtooth deflection current generator

Abstract

A line sawtooth deflection current generator with modulating means for the purpose of correcting the amplitude variations of the current produced, the said modulating means including a stage operating in the switching mode.

What is claimed is: 
     
       1. A circuit for generating a line frequency sawtooth deflection current having trace and retrace periods through a deflection coil, said circuit comprising a first sawtooth network comprising a trace capacitor adapted to be coupled to said coil, and a retrace capacitor coupled to said trace capacitor, a second sawtooth network series coupled to said first network and comprising a diode, a second coil coupled to said diode, a second trace capacitor coupled to said second coil, and a second retrace capacitor coupled to said second trace capacitor, means coupled to said networks for receiving a supply voltage from a source, a controlled switch which is non-conducting during the retrace period, the series arrangement of said networks being coupled in parallel across the controlled switch, and a switching mode modulating means for varying the voltage across one of the trace capacitors for modulating the magnitude of the line sawtooth deflection current through said deflection coil. 
     
     
       2. A circuit as calimed in claim 1, wherein said switching mode means includes a supply input, a switching device, and means for applying thereto controlling periodic pulses for alternately driving said switching device into a conducting state and a non-conducting state and for adjusting the duration of the controlling pulses depending on the nature of the magnitude of the modulation required at the supply input of said switching mode means. 
     
     
       3. A circuit as claimed in claim 2, wherein the frequency of said controlling pulses comprises the line frequency. 
     
     
       4. A circuit as claimed in claim 2, wherein said applying and adjusting means comprises a comparator means for comparing a waveform at the controlling pulse frequency with a signal of the form required to give the desired modulation of said deflection current. 
     
     
       5. A circuit as claimed in claim 4, wherein said waveform at the controlling pulse frequency is compared with a parabolic signal at field frequency, said voltage at said one of said trace capacitors being modulated such that the magnitude of the line deflection current is changed over a field period to provide correction for pin-cushion distortion in the East-West direction on a television display tube associated with said line deflection coil. 
     
     
       6. A circuit as claimed in claim 4, wherein said switching mode means comprises a forward converter type, said comparator means including means for making an additional comparison with the voltage at the input of said switching mode means. 
     
     
       7. A circuit as claimed in claim 1, wherein said switching mode means comprises a power supply having an input coupled to said one trace capacitor and an output adapted to be coupled to a load, a voltage having a predetermined value being produced across said load due to the output of said switching mode means. 
     
     
       8. A circuit as claimed in claim 7, wherein said load voltage is substantially constant. 
     
     
       9. A circuit as claimed in claim 8, wherein said load includes a constant reference voltage diode. 
     
     
       10. A circuit as claimed in claim 7, further comprising a voltage source means coupled to said load for defining the voltage across said load. 
     
     
       11. A circuit as claimed in claim 10, further comprising a transformer having a winding coupled to said switching mode means, and wherein said voltage source comprises a rectifying circuit coupled to said winding. 
     
     
       12. A circuit as claimed in claim 1, wherein said switching mode means includes a choke means for integrating the switching current and for isolating the line deflection circuit from said switching mode means. 
     
     
       13. A circuit as claimed in claim 7, wherein said load comprises a circuit required power, at least part of the power requirements for said circuit being provided by said switching mode means. 
     
     
       14. A circuit for generating a line frequency sawtooth deflection current having trace and retrace periods through a deflection coil, said circuit comprising a first sawtooth network comprising a trace capacitor adapted to be coupled to said coil and a retrace capacitor coupled to said trace capacitor, a second sawtooth network series coupled to said first network and comprising a diode, a second coil coupled to said diode, a second trace capacitor coupled to said second coil and a second retrace capacitor coupled to said second trace capacitor, means coupled to said networks for receiving a supply voltage from a source, a controlled switch which is non-conducting during the retrace period, the series arrangement of said networks being coupled in parallel across the controlled switch, and a switching mode modulating means for varying the voltage across one of the trace capacitors for modulating the magnitude of the line sawtooth deflection current through said deflection coil, said modulating means having supply input terminals coupled to said one of said trace capacitors and supply output terminals adapted to be coupled to a load. 
     
     
       15. A circuit as claimed in claim 14, wherein said switching mode means includes a switching device, and means for applying thereto controlling periodic pulses for alternately driving said switching device into a conducting state and a non-conducting state and for adjusting the duration of the controlling pulses depending on the nature and the magnitude of the modulation required at the supply input terminals of said switching mode means. 
     
     
       16. A circuit as claimed in claim 15, wherein the frequency of said controlling pulses comprises the line frequency. 
     
     
       17. A circuit as claimed in claim 15, wherein said applying and adjusting means comprises a comparator means for comparing a waveform at the controlling pulse frequency with a signal of the form required to give the desired modulation of said deflection current. 
     
     
       18. A circuit as claimed in claim 17, wherein said waveform at the controlling pulse frequency is compared with a parabolic signal at field frequency, said voltage at said one of said trace capacitors being modulated such that the magnitude of the line deflection current is changed over a field period to provide correction for pin-cushion distortion in the East-West direction on a television display tube associated with said line deflection coil. 
     
     
       19. A circuit as claimed in claim 17, wherein said switching mode means comprises a forward converter type, said comparator means including means for making an additional comparison with the voltage at the input of said switching mode means. 
     
     
       20. A circuit as claimed in claim 14, wherein said switching mode means includes a choke means for integrating the switching current and for isolating the line deflection circuit from said switching mode means.